Method for making aluminosilicate ZSM-12

ABSTRACT

An aluminosilicate ZSM-12 may be prepared de novo in a small crystalline form from a reaction mixture containing a source of silica and a source of alumina. A small crystalline form of aluminosilicate ZSM-12 may also be prepared from a small crystalline form of borosilicate ZSM-12 by replacement of boron in the borosilicate ZSM-12 framework with aluminum. The aluminosilicate ZSM-12 is useful as an isomerization selective catalyst in processes such as isomerization dewaxing hydrocarbon feedstocks.

FIELD OF THE INVENTION

The present invention relates to aluminosilicate ZSM-12 compositions,methods for directly and indirectly preparing aluminosilicate ZSM-12,and uses for ZSM-12.

BACKGROUND OF THE INVENTION

Molecular sieves are a class of important materials used in the chemicalindustry for processes such as gas stream purification and hydrocarbonconversion processes. Molecular sieves are porous solids havinginterconnected pores of different sizes. Molecular sieves typically havea one-, two- or three-dimensional crystalline pore structure havingpores of one or more molecular dimensions that selectively adsorbmolecules that can enter the pores, and exclude those molecules that aretoo large. The pore size, pore shape, interstitial spacing or channels,composition, crystal morphology and structure are a few characteristicsof molecular sieves that determine their use in various hydrocarbonadsorption and conversion processes.

For the petroleum and petrochemical industries, the most commerciallyuseful molecular sieves are known as zeolites. A zeolite is analuminosilicate having an open framework structure formed from comersharing the oxygen atoms of [SiO₄] and [AlO₄] tetrahedra or octahedra.Mobile extra framework cations reside in the pores for balancing chargesalong the zeolite framework. These charges are a result of substitutionof a tetrahedral framework cation (e.g. Si⁴⁺) with a trivalent orpentavalent cation. Extra framework cations counter-balance thesecharges preserving the electroneutrality of the framework, and thesecations are exchangeable with other cations and/or protons.

Synthetic aluminosilicate molecular sieves, particularly zeolites, aretypically synthesized by mixing sources of alumina and silica in anaqueous media, often in the presence of a structure directing agent ortemplating agent. The structure of the molecular sieve formed isdetermined in part by solubility of the various sources,silica-to-alumina ratio, nature of the cation, synthesis conditions(temperature, pressure, mixing agitation), order of addition, type oftemplating agent, and the like.

Molecular sieves identified by the International Zeolite Associate (IZA)as having the structure code MTW are known. ZSM-12 is a knowncrystalline MTW material, and is useful in many processes, includingvarious catalytic reactions. Accordingly, there is a continued need fornew methods for making ZSM-12, particularly small crystal forms of thismaterial.

Further, there is a current need to identify molecular sieves that aresuitable for catalystic n-paraffin isomerization. High-qualitylubricating oils are required for the operation of modern machinery andautomobiles. Most lubricating oil feedstocks must be dewaxed in order toproduce high-quality lubricating oils. Catalytic dewaxing has advantagesover solvent extraction of waxes, and the former is a valuablehydrocarbon processing technique. Catalytic dewaxing may be accomplishedby cracking and/or isomerization of n-paraffins in the feedstocks.

Some prior art catalytic dewaxing processes operate at relatively hightemperatures and pressures, resulting in extensive cracking and theproduction of lower value light gases. Therefore, catalytic dewaxing byisomerization of n-paraffins at lower temperatures is desirable.Accordingly, there is a continued need for new catalysts having improvedhydrocarbon isomerization selectivity and conversion.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided analuminosilicate ZSM-12 molecular sieve having a mole ratio of between 30and 100 of silicon oxide to aluminum oxide and having, aftercalcination, the powder X-ray diffraction (XRD) lines of Table 5.

The aluminosilicate ZSM-12 is prepared by contacting undercrystallization conditions: (1) at least one source of silicon oxide;(2) at least one source of aluminum oxide; (3) at least one source of anelement selected from Groups 1 and 2 of the Periodic Table; (4)hydroxide ions; (5) 1,6-bis(2,3-dimethylimidazolium)hexane cations; and(6) optionally, a second nitrogen-containing structure directing agentsuitable for synthesizing ZSM-12.

The aluminosilicate ZSM-12 synthesized per the teachings herein has acomposition, as-synthesized and in the anhydrous state, in terms of moleratios, as follows:

SiO₂/Al₂O₃ 30-100 (Q + A)/SiO₂ 0.015-0.06  M/SiO₂  0-0.1

wherein:

(1) M is at least one element selected from Groups 1 and 2 of thePeriodic Table;

(2) Q is cationic 1,6-bis(2,3-dimethylimidazolium)hexane, and Q>0; and

(3) A is a second nitrogen-containing structure directing agent, andA≧0.

According to a further aspect of the present invention there is provideda method of preparing aluminosilicate ZSM-12 by:

(a) preparing a reaction mixture containing: (1) at least one source ofsilicon oxide; (2) at least one source of boron oxide; (3) at least onesource of an element selected from Groups 1 and 2 of the Periodic Table;(4) hydroxide ions; (5) cationic 1,4-bis(trimethylammonium)butane orcationic 1,4-bis(N-methylpiperidinium)butane as the structure directingagent; and (6) water;

b) maintaining the reaction mixture under crystallization conditionssufficient to form crystals of borosilicate ZSM-12; and

c) replacing boron in the framework of the borosilicate ZSM-12 withaluminum to provide aluminosilicate ZSM-12.

The present invention also includes a process for converting ahydrocarbonaceous feed by contacting the feed under isomerizationconditions with a ZSM-12 molecular sieve having a mole ratio of between30 and 100 of silicon oxide to aluminum oxide and having, aftercalcination, the powder XRD lines of Table 5.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a powder XRD pattern of impure ZSM-12 prepared according toComparative Example 1;

FIG. 2 shows a powder XRD pattern of pure aluminosilicate ZSM-12prepared according to Examples 2-4 and 6 of the present invention;

FIG. 3 shows powder XRD patterns of borosilicate ZSM-12 preparedaccording to Examples 7-9 of the present invention, in comparison withthe pattern for a conventional (standard) sample of aluminosilicateZSM-12;

FIGS. 4 and 5 show a scanning electron micrograph of the borosilicateZSM-12 prepared according to Example 8 of the present invention; and

FIG. 6 shows a powder XRD pattern of the aluminosilicate ZSM-12 preparedaccording to Example 11 of the present invention, in comparison with thepattern for borosilicate ZSM-12.

DETAILED DESCRIPTION OF THE INVENTION

Introduction

The term “active source” means a reagent or precursor material capableof supplying at least one element in a form that can react and which maybe incorporated into a zeolite structure. The terms “source” and “activesource” may be used interchangeably herein.

The term “Periodic Table” refers to the version of IUPAC Periodic Tableof the Elements dated Jun. 22, 2007, and the numbering scheme for thePeriodic Table Groups is as described in Chemical and Engineering News,63(5), 27 (1985).

The term “isomerization conditions” may be used herein to refer to oneor more sets of physical and/or chemical parameters, such as a suitabletemperature, pressure, feed rate, and catalyst composition, that allowor promote the isomerization of n-paraffins in a hydrocarbonaceous feed.

The term “isomerization selectivity” may be used herein to refer to thepercentage of converted n-C₁₀+ alkanes in a hydrocarbon feed that areisomerized to isoparaffins in the product of a catalytic hydrocarbonconversion process.

Isoparaffin (i-) to normal (n-) paraffin ratios (i/n ratios) refer toweight ratios unless otherwise noted.

Where permitted, all publications, patents and patent applications citedin this application are herein incorporated by reference in theirentirety, to the extent such disclosure is not inconsistent with thepresent invention.

Unless otherwise specified, the recitation of a genus of elements,materials or other components, from which an individual component ormixture of components can be selected, is intended to include allpossible sub-generic combinations of the listed components and mixturesthereof. Also, the term “include” and its variants, are intended to beNon-limiting, such that recitation of items in a list is not to theexclusion of other like items that may also be useful in the materials,compositions, and methods of this invention.

Aluminosilicate and Borosilicate ZSM-12 Reaction Mixtures

In preparing aluminosilicate ZSM-12 (Al-ZSM-12), a1,6-bis(2,3-dimethylimidazolium)hexane dication is used, either alone orin combination with a second nitrogen-containing structure directingagent (designated composition variable “A” herein below). The1,6-bis(2,3-dimethylimidazolium)hexane useful for making Al-ZSM-12 isrepresented by the following structure (1):

In general, Al-ZSM-12 is prepared by:

(a) preparing a reaction mixture containing: (1) at least one source ofsilicon oxide; (2) at least one source of aluminum oxide; (3) at leastone source of an element selected from Groups 1 and 2 of the PeriodicTable; (4) hydroxide ions; (5) 1,6-bis(2,3-dimethylimidazolium)hexanecations; and (6) optionally, a second nitrogen-containing structuredirecting agent; and

(b) maintaining the reaction mixture under conditions sufficient to formcrystals of the Al-ZSM-12 molecular sieve.

The composition of the reaction mixture from which the aluminosilicateZSM-12 molecular sieve is formed, in terms of molar ratios, isidentified in Table 1 below:

TABLE 1 Reactants Broad Preferred SiO₂/Al₂O₃   30-100 30-60 (Q + A)/SiO₂0.03-0.8 0.03-0.4  Q/A 0.05-∞ 0.05-0.11 M/SiO₂ 0.05-1 0.15-0.3  OH⁻/SiO₂ 0.1-1 0.2-0.5 H₂O/SiO₂   20-80 30-70wherein:

(1) M is at least one element selected from Groups 1 and 2 of thePeriodic Table;

(2) Q is cationic 1,6-bis(2,3-dimethylimidazolium)hexane, and Q>0; and

(3) A is a second nitrogen-containing structure directing agent, andA≧0.

It should be noted that the Q/A molar ratio includes the case wherethere is no second nitrogen-containing structure directing agent (A) inthe reaction mixture. In that case the reaction mixture only containscationic 1,6-bis(2,3-dimethylimidazolium)hexane (Q) as the structuredirecting agent. In one subembodiment, the Q/A mole ratio is 0.05 to0.3. In another subembodiment, the Q/A mole ratio is 0.05 to 0.2. Inanother subembodiment, the Q/A mole ratio is 0.05 to about 0.11.

According to one aspect of the instant invention, a small crystal formof aluminosilicate ZSM-12 can be prepared from a small crystal form ofborosilicate ZSM-12 by post-synthetic replacement of the boron in theborosilicate ZSM-12 framework with aluminum. The small crystal form ofthe precursor borosilicate ZSM-12 may be prepared as described below.Then, replacement of boron in the borosilicate ZSM-12 with aluminumprovides an alternative, yet facile, route to the synthesis of a lowSi/Al ratio aluminosilicate ZSM-12 of small crystal size.

Replacement of boron in borosilicate ZSM-12 with aluminum may be readilyachieved by suitable treatment of the borosilicate ZSM-12 with analuminum salt, such as aluminum nitrate. In an embodiment, theproportion of boron in borosilicate ZSM-12 that may be replaced withaluminum according to the invention may be in the range of from aboutzero (0) to about 100%, typically from about 75% to about 100%, oftenfrom about 85% to about 100%. In a subembodiment, at least about 50% ofthe boron in the borosilicate framework is replaced with aluminum.

In preparing borosilicate ZSM-12 (B-ZSM-12), a1,4-bis(trimethylammonium)butane dication or a1,4-bis(N-methylpiperidinium)butane dication, represented by structures2 and 3 below, respectively, is used as the structure directing agent.

In general, borosilicate ZSM-12 is prepared by:

(a) preparing a reaction mixture containing: (1) at least one source ofsilicon oxide; (2) at least one source of boron oxide; (3) at least onesource of an element selected from Groups 1 and 2 of the Periodic Table;(4) hydroxide ions; (5) cationic 1,4-bis(trimethylammonium)butane orcationic 1,4-bis(N-methylpiperidinium)butane as the structure directingagent; and (6) water; and

(b) maintaining the reaction mixture under conditions sufficient to formcrystals of the borosilicate ZSM-12.

The composition of the reaction mixture from which the borosilicateZSM-12 molecular sieve is formed, in terms of molar ratios, isidentified in Table 2 below:

TABLE 2 Reactants Broad Preferred SiO₂/B₂O₃ 10-100 20-60 X/SiO₂0.05-1    0.1-0.4 M/SiO₂ 0.1-1   0.2-0.4 OH⁻/SiO₂ 0.1-0.6  0.2-0.4H₂O/SiO₂ 20-100 30-60wherein M is at least one element selected from Groups 1 and 2 of thePeriodic Table, and X is cationic 1,4-bis(trimethylammonium)butane orcationic 1,4-bis(N-methylpiperidinium)butane.

Sources of silicon oxide useful herein include fumed silica,precipitated silicates, silica hydrogel, silicic acid, colloidal silica,tetra-alkyl orthosilicates (e.g. tetraethyl orthosilicate), and silicahydroxides.

Sources of aluminum oxide useful herein include aluminates, alumina, andaluminum compounds such as AlCl₃, Al₂SO₄, Al(OH)₃, kaolin clays, andother zeolites.

Sources of boron oxide useful herein include borosilicate glasses,alkali borates, boric acid, borate esters, and certain zeolites.Non-limiting examples of a source of boron oxide include potassiumtetraborate decahydrate and boron beta zeolite (B-beta zeolite).

A source of element M may be any M-containing compound which is notdetrimental to the crystallization process. M-containing compounds mayinclude oxides, hydroxides, nitrates, sulfates, halides, oxalates,citrates and acetates thereof. In one subembodiment, compositionalvariable M is sodium (Na) or potassium (K). In a subembodiment, anM-containing compound is an alkali metal halide, such as a bromide,iodide or potassium.

The molecular sieve reaction mixture can be supplied by more than onesource. Also, two or more reaction components can be provided by onesource. As an example, borosilicate molecular sieves may be synthesizedfrom boron-containing beta molecular sieves, as taught in U.S. Pat. No.5,972,204, issued Oct. 26, 1999 to Corma et al.

The optional second nitrogen-containing structure directing agent (A)used in the reaction mixture for synthesizing Al-ZSM-12 is an organicnitrogen containing compound, such as a linear or cyclic quaternary ordiquaternary ammonium compound, suitable for synthesizing MTW-typematerials. Structure directing agents suitable for synthesizing ZSM-12are known in the art. (See, for example, Handbook of Molecular Sieves,Szostak, Van Nostrand Reinhold, 1992; U.S. Pat. No. 4,585,639, issuedApr. 29, 1986 to Szostak; and U.S. Pat. No. 4,482,531, issued Nov. 13,1984 to Kuehl). Exemplary structure directing agents include:tetraalkylammonium cations such as methyltriethylammonium cations andtetraethylammonium cations; cationic dimethylpyrrolidinium; cationicdimethyl piperidinium; and cationic dimethylpyridinium.

The reaction mixture can be prepared either batch-wise or continuously.Crystal size, crystal morphology, and crystallization time of thealuminosilicate ZSM-12 of the present invention may vary with the natureof the reaction mixture and the crystallization conditions.

The structure directing agents (Q and A) are typically associated withanions which may be any anion that is not detrimental to the formationof the molecular sieve. Representative anions include chloride, bromide,iodide, hydroxide, acetate, sulfate, tetrafluoroborate, carboxylate, andthe like.

Crystallization and Post-Synthesis Treatment

In practice, ZSM-12 is synthesized by: (a) preparing a reaction mixtureas described hereinabove; and (b) maintaining the reaction mixture undercrystallization conditions sufficient to form crystals of the molecularsieve. The reaction mixture is maintained at an elevated temperatureuntil crystals of the molecular sieve are formed. The hydrothermalcrystallization of the molecular sieve is usually conducted underpressure, and usually in an autoclave so that the reaction mixture issubject to autogenous pressure, typically at a temperature from about140° C. to about 190° C., and usually from about 150° C. to about 170°C. for the aluminosilicate form, and from about 140° C. to about 200°C., and usually from about 150° C. to about 170° C. for the borosilicateform.

The reaction mixture may be subjected to mild stirring or agitationduring the crystallization step. It will be understood by a personskilled in the art that the ZSM-12 molecular sieve described herein maycontain one or more trace impurities, such as amorphous materials,phases having framework topologies which do not coincide with thezeolite, and/or other impurities (e.g., organic hydrocarbons).

During the hydrothermal crystallization step, crystals of ZSM-12 can beallowed to nucleate spontaneously from the reaction mixture. The use ofcrystals of the zeolite as seed material can be advantageous indecreasing the time necessary for complete crystallization to occur. Inaddition, seeding can lead to an increased purity of the productobtained by promoting the nucleation and/or formation of the zeoliteover any undesired phases. When used as seeds, seed crystals aretypically added in an amount from about 0.5% to about 5% of the weightof the source of silicon dioxide used in the reaction mixture.

Once the crystals have formed, the solid product may be separated fromthe reaction mixture by mechanical separation techniques such asfiltration. The crystals are water washed and then dried to obtain“as-synthesized” crystals. The drying step can be performed atatmospheric pressure or under vacuum.

ZSM-12 may be used as-synthesized, but typically the zeolite will bethermally treated (calcined). The term “as-synthesized” refers to theZSM-12 in its form after crystallization, prior to removal of thestructure directing agent and/or element M. The organic material can beremoved by thermal treatment (e.g., calcination), preferably in anoxidative atmosphere (e.g., air, or another gas with an oxygen partialpressure greater than 0 kPa), at a temperature (readily determinable byone skilled in the art) sufficient to remove the organic material fromthe zeolite. The organic material can also be removed by photolysistechniques, e.g., by exposing an SDA-containing zeolite product to lightor electromagnetic radiation that has a wavelength shorter than visiblelight under conditions sufficient to selectively remove organic materialfrom the zeolite, substantially as described in U.S. Pat. No. 6,960,327to Navrotsky and Parikh.

Usually, it may also be desirable to remove alkali metal cations fromthe ZSM-12 by ion-exchange and to replace the alkali metal cations withhydrogen, ammonium, or a desired metal ion. The ZSM-12 can be combinedwith various metals, such as a metal selected from Groups 8-10 of thePeriodic Table, including Pt, Pd, Ni, Rh, Ir, Ru, Os, or combinationsthereof, by impregnation, or physical admixture, and the like, as wellas ion-exchange.

Following ion-exchange, e.g., palladium exchange, the zeolite istypically washed with water and dried at temperatures ranging from 90°C. to about 120° C. After washing, the zeolite can be calcined in air,steam, or inert gas at a temperature ranging from about 315° C. to about650° C. for periods ranging from about 1 to about 24 hours, or more, toproduce a catalytically active product particularly useful inhydrocarbon isomerization and dewaxing processes.

Characterization of the Molecular Sieve

Aluminosilicate ZSM-12 prepared according to the teachings herein has acomposition, as-synthesized and in the anhydrous state, as shown inTable 3 in terms of mole ratios:

TABLE 3 SiO₂/Al₂O₃ 30-100 (Q + A)/SiO₂ 0.015-0.06  M/SiO₂  0-0.1wherein M, Q and A are as described hereinabove.

Aluminosilicate ZSM-12 prepared according to the present invention has aSiO₂/Al₂O₃ mole ratio generally from about 30 to about 100, and in onesubembodiment from about 30 to about 80, and in another subembodimentfrom about 30 to about 60. Aluminosilicate ZSM-12 of the presentinvention typically crystallizes as aggregates of intergrown crystals,wherein each aggregate contains a plurality of elongated crystallites.Each individual crystallite may be needle-like with a width in the rangefrom about 15 to about 25 nm and a length in the range from about 60 toabout 80 nm, with average dimensions of the crystallites of about 20 nmby about 60 nm.

ZSM-12 products synthesized by the methods described herein arecharacterized by their powder X-ray diffraction (XRD) pattern. Minorvariations in the diffraction pattern can result from variations in themole ratios of the framework species of the particular borosilicateZSM-12 sample due to changes in lattice constants. In addition,sufficiently small crystals will affect the shape and intensity ofpeaks, leading to significant peak broadening. Minor variations in thediffraction pattern can also result from variations in the structure ofthe organic template used in the zeolites preparation. Calcination canalso cause minor shifts in the powder XRD pattern. Notwithstanding theseminor perturbations, the basic crystal lattice structure remainsunchanged.

The XRD pattern lines of Table 4 are representative of as-synthesizedaluminosilicate ZSM-12 made in accordance with the teachings presentedherein.

TABLE 4 Characteristic powder XRD peaks for as-synthesizedaluminosilicate ZSM-12 2 Theta^((a)) d-spacing (Angstroms) RelativeIntensity^((b)) 7.48 11.82 M 8.80 10.04 W 18.74 4.73 W 19.10 4.64 W19.93 4.45 W 20.85 4.26 VS 21.77 4.08 W 22.36 3.97 W 22.98 3.87 S 23.243.82 W 25.32 3.52 W 25.72 3.46 W 26.24 3.39 W 26.80 3.32 W 27.89 3.20 W29.21 3.05 W 30.81 2.90 W 35.61 2.52 W ^((a))±0.25 ^((b))Based on arelative intensity scale in which the strongest line in the X-raypattern is assigned a value of 100: W (weak) is less than 20; M (medium)is between 20 and 40; S (strong) is between 40 and 80; VS (very strong)is greater than 80.

The XRD pattern lines of Table 5 are representative of calcinedaluminosilicate ZSM-12 made in accordance with the teachings presentedherein.

TABLE 5 Characteristic powder XRD peaks for calcined aluminosilicateZSM-12 2 Theta^((a)) d-spacing (Angstroms) Relative Intensity^((b)) 7.5111.76 M 8.86 9.98 W 14.81 5.98 W 15.28 5.80 W 18.75 4.73 W 19.11 4.64 W20.03 4.43 W 20.91 4.25 VS 21.98 4.04 W 22.42 3.96 W 22.98 3.88 W 23.243.82 M 25.21 3.53 W 25.78 3.45 W 26.33 3.38 W 26.86 3.32 W 27.99 3.19 W29.33 3.04 W 30.88 2.89 W 35.71 2.51 W 36.97 2.43 W 38.57 2.33 W^((a))±0.25 ^((b))Based on a relative intensity scale in which thestrongest line in the X-ray pattern is assigned a value of 100: W (weak)is less than 20; M (medium) is between 20 and 40; S (strong) is between40 and 80; VS (very strong) is greater than 80.

Borosilicate ZSM-12 prepared according to the present invention has acomposition, as-synthesized and in the anhydrous state, as shown inTable 6, in terms of mole ratios, wherein X and M are as describedhereinabove:

TABLE 6 SiO₂/B₂O₃ 40-100 X/SiO₂ 0.02-0.06  M/SiO₂  0-0.1

Borosilicate ZSM-12 of the present invention typically crystallizes asellipsoidal aggregates of intergrown crystals, wherein the aggregateshave a length of about 1 μm and a width in the range from about 0.3 μmto about 0.5 μm.

The XRD pattern lines of Table 7 are representative of as-synthesizedborosilicate ZSM-12 made in accordance with the teachings presentedherein.

TABLE 7 Characteristic powder XRD peaks for as-synthesized B-ZSM-12 2Theta^((a)) d-spacing (Angstroms) Relative Intensity^((b)) 7.61 11.61 M8.86 9.97 W 19.12 4.64 W 20.31 4.37 W 21.17 4.19 VS 22.10 4.02 W 22.753.90 W 23.30 3.81 S 25.51 3.49 W 26.10 3.41 W 26.62 3.35 W 26.98 3.30 W28.29 3.15 W 29.61 3.02 W ^((a))±0.25 ^((b))Based on a relativeintensity scale in which the strongest line in the X-ray pattern isassigned a value of 100: W (weak) is less than 20; M (medium) is between20 and 40; S (strong) is between 40 and 80; VS (very strong) is greaterthan 80.

The powder XRD patterns and data presented herein were collected bystandard techniques. The radiation was CuK-α radiation. The peak heightsand the positions, as a function of 2θ where θ is the Bragg angle, wereread from the relative absolute intensities of the peaks, and d, theinterplanar spacing in Angstroms corresponding to the recorded lines,can be calculated.

Applications for Aluminosilicate ZSM-12

Catalyst Compositions Comprising Al-ZSM-12

Catalyst compositions comprising aluminosilicate ZSM-12 of the presentinvention may have a composition, in terms of weight percent, as shownin Table 8:

TABLE 8 Component Broad Secondary aluminosilicate ZSM-12 1-99% 15-50%binder 1-99% 50-85% Group 8-10 metals(s) and other elements 0-5% 0.5-1.5%

For commercial applications as a catalyst, the aluminosilicate ZSM-12may be formed into a suitable size and shape. This forming can be doneby techniques such as pelletizing, extruding, and combinations thereof.In the case of forming by extrusion, extruded materials can becylinders, trilobes, fluted, or have other shapes, which may be axiallysymmetrical, and that promote diffusion and access of feed materials tointerior surfaces of the aluminosilicate ZSM-12 extrusion product.

In preparing catalysts for use in processes of the present invention,the aluminosilicate ZSM-12 crystals can be composited with bindersresistant to the temperatures and other conditions employed inhydrocarbon conversion processes. Binders may also be added to improvethe crush strength of the catalyst.

The binder material may comprise one or more refractory oxides, whichmay be crystalline or amorphous, or can be in the form of gelatinousprecipitates, colloids, sols, or gels. Silica in the form of a silicasol is a preferred binder. A preferred silica sol has about 30 wt %silica and a particle size of about 7-9 nm in diameter, which providescatalysts having good attrition resistance and excellent crushstrengths.

Forming pellets or extrudates from molecular sieves, including the smallcrystal forms of aluminosilicate ZSM-12 useful in this invention,generally involves using extrusion aids and viscosity modifiers inaddition to binders. These additives are typically organic compoundssuch as cellulose based materials, for example, METHOCEL cellulose ether(Dow Chemical Co.), ethylene glycol, and stearic acid. Such compoundsare known in the art. It is important that these additives do not leavea detrimental residue, i.e., one with undesirable reactivity or one thatcan block pores of the zeolite, after pelletizing.

Methods for preparing catalyst compositions are well known to thoseskilled in the art and include such conventional techniques as spraydrying, pelletizing, extrusion, various sphere-making techniques, andthe like.

The relative proportions of the aluminosilicate ZSM-12 and binder canvary widely. Generally, the aluminosilicate ZSM-12 content ranges fromabout 1 to about 99 weight percent (wt %) of the dry composite, usuallyin the range of from about 5 to about 95 wt % of the dry composite, andmore typically from about 15 to about 50 wt % of the dry composite.

The catalyst can optionally contain one or more metals selected fromGroups 8-10 of the Periodic Table. In one subembodiment, the catalystcontains a metal selected from the group consisting of Pt, Pd, Ni, Rh,Ir, Ru, Os, and mixtures thereof. In another subembodiment, the catalystcontains palladium (Pd) or platinum (Pt). For each embodiment describedherein, the Group 8-10 metal content of the catalyst may be generally inthe range of from 0 to about 10 wt %, typically from about 0.05 to about5 wt %, usually from about 0.1 to about 3 wt %, and often from about 0.3to about 1.5 wt %. In an embodiment, the aluminosilicate ZSM-12 can bepalladium exchanged.

Additionally, other elements may be used in combination with the metalselected from Groups 8-10 of the Periodic Table. Examples of such “otherelements” include Sn, Re, and W. Examples of combinations of elementsthat may be used in catalyst materials of the present invention include,without limitation, Pt/Sn, Pt/Pd, Pt/Ni, and Pt/Re. These metals orother elements can be readily introduced into the aluminosilicate ZSM-12composite using one or more of various conventional techniques,including ion-exchange, pore-fill impregnation, or incipient wetnessimpregnation. Reference to the catalytically active metal or metals isintended to encompass such metal or metals in the elemental state or insome form such as an oxide, sulfide, halide, carboxylate, and the like.

Selective Isomerization of n-paraffins to Isoparaffins

Aluminosilicate or borosilicate ZSM-12, prepared according to the novelmethods described herein may be useful in catalytic hydrocarbonconversion processes involving n-paraffin selective isomerization. Incontrast, “cracking” refers to processes or reactions that decrease themolecular weight of hydrocarbons by breaking them into smallercomponents.

Catalyst compositions comprising aluminosilicate ZSM-12 of the inventionshow a high propensity for isomerization of n-paraffins with highconversion at relatively low temperatures (e.g., 260° C. to 280° C.),and hence a low propensity for cracking. Moreover, catalyst compositionsof the present invention are highly selective for the production ofdimethyl isoparaffins over monomethyl isoparaffins (see, e.g., Table 9).

According to the present invention, a process for convertinghydrocarbons includes contacting a hydrocarbonaceous feed underisomerization conditions with aluminosilicate ZSM-12 synthesized asdescribed herein, and having a SiO₂/Al₂O₃ mole ratio from about 30 toabout 100, and in one subembodiment from about 30 to about 80, and inanother subembodiment, from about 30 to about 60.

Catalyst compositions of the instant invention may be used to dewax avariety of feedstocks ranging from relatively light distillatefractions, such as kerosene and jet fuel, up to high boiling stocks suchas whole crude petroleum, reduced crudes, vacuum tower residua, cycleoils, synthetic crudes (e.g., shale oils, tars and oil, etc.), gas oils,vacuum gas oils, foots oils, Fischer-Tropsch derived waxes, and otherheavy oils. Straight chain n-paraffins either alone or with onlyslightly branched chain paraffins having 16 or more carbon atoms aresometimes referred to herein as waxes.

The feedstock will often be a C₁₀₊ feedstock generally boiling aboveabout 177° C. Processes of the present invention may be particularlyuseful with waxy distillate stocks such as middle distillate stocksincluding gas oils, kerosenes, and jet fuels, lubricating oil stocks,heating oils and other distillate fractions whose pour point andviscosity need to be maintained within certain specification limits.Lubricating oil stocks will generally boil above 230° C., more usuallyabove 315° C. Hydroprocessed stocks are a convenient source of stocks ofthis kind and also of other distillate fractions since they normallycontain significant amounts of waxy n-paraffins.

Feedstocks for processes of the present invention may contain paraffins,olefins, naphthenes, aromatic and heterocyclic compounds and may have asubstantial proportion of higher molecular weight n-paraffins andslightly branched paraffins which contribute to the waxy nature of thefeedstock. During the processing, the n-paraffins and the slightlybranched paraffins may undergo a relatively low degree of cracking athigh conversion.

Examples of some typical feedstocks which may be used in processes ofthe instant invention include hydrotreated or hydrocracked gas oils,hydrotreated lube oil raffinates, brightstocks, lubricating oil stocks,synthetic oils, foots oils. Fischer-Tropsch synthesis oils, high pourpoint polyolefins, normal alphaolefin waxes, slack waxes, de-oiled waxesand microcrystalline waxes.

In an embodiment, the present invention provides processes forhydroconverting a hydrocarbonaceous feed which comprises C₁₀₊n-paraffins. Such processes may comprise contacting the feed in thepresence of hydrogen and under isomerization conditions with a catalystcomposition comprising aluminosilicate ZSM-12 to provide an isoparaffinproduct with an isomerization selectivity of at least about 80% atgreater than about 90% conversion of the feed. The aluminosilicateZSM-12 may be prepared, and may have characteristics and features, asdescribed herein.

The conditions for isomerization dewaxing processes of the presentinvention generally include a temperature typically within a range fromabout 240° C. to about 320° C., usually from about 255° C. to about 290°C., often from about 260° C. to about 280° C.; and a pressure from about15 to about 5000 psig, typically from about 50 to about 3000 psig, andoften from about 100 to about 2500 psig. The contacting of the feed withthe catalyst is generally carried out in the presence of hydrogen. Thehydrogen to hydrocarbon ratio is generally within a range from about2000 to about 10,000 standard cubic feet H₂ per barrel of hydrocarbon,and typically from about 2500 to about 5000 standard cubic feet H₂ perbarrel of hydrocarbon. The liquid hourly space velocity (LHSV) duringcontacting is generally from about 0.1 to about 20, more usually fromabout 0.1 to about 5, and often from about 0.5 to about 5.

According to an aspect of the invention, n-hexadecane may be used as amodel compound, to represent a “heavier” n-alkane feed, for theidentification of catalysts that selectively isomerize heavier (e.g.,C₁₀₊) normal paraffins providing relatively high levels of isoparaffinproducts, with much lower levels of cracking. In a subembodiment,n-hexadecane may be used to identify n-paraffin isomerization selectivecatalysts that isomerize n-C₁₀₊ alkanes to an isoparaffin productcomprising predominantly dimethyl isoalkanes.

Isomerization dewaxing processes of the invention provide an isoparaffinconversion product comprising a mixture of monomethyl- and dimethylisoalkanes. For a hydrocarbon feed comprising n-hexadecane, processes ofthe present invention provide an isoparaffin product which may includedimethyl C₁₄ alkanes together with monomethyl C₁₅ alkanes, wherein thedimethyl isoalkanes may predominate over the monomethyl isoalkanes.Stated alternatively, dimethyl isoalkanes may comprise more than 50% ofthe isoalkanes in the product. In an embodiment, at a temperature fromabout 260° C. to about 280° C. the ratio of dimethyl isoparaffins tomonomethyl isoparaffins in the product is at least about 2. In someembodiments, the dimethyl isoalkanes may generally comprise more thanabout 66% of the isoalkanes in the product, typically more than about70%, often at least about 75%, and in one embodiment about 80%, of theisoalkanes in the product.

In one embodiment of the present invention, at a temperature from about260° C. to about 280° C. a selective isomerization catalyst comprisingaluminosilicate ZSM-12 converts at least about 96% of n-paraffins in thefeed to provide a product comprising isoparaffins with an isomerizationselectivity of at least about 85% (≦15% cracking). In a subembodiment,the feed may be contacted with the catalyst under isomerizationconditions comprising a temperature in the range of about 265° C. toabout 270° C. to provide at least about 95% conversion of n-hexadecanewith an isomerization selectivity of at least about 88% (≦12% cracking).

In a subembodiment, a catalyst composition of the present inventionunder isomerization conditions at a temperature of about 260-280° C.provides at least about 96% conversion of n-hexadecane in the feed withan iso-C₁₆ yield of at least about 75%. In another subembodiment, forexample, the catalyst composition may provide an iso-C₁₆ yield in therange from about 84% to about 88%.

In another embodiment, at a temperature of about 280° C. anisomerization selective catalyst of the present invention provides a C₁₀alkane product from an n-hexadecane feed, wherein the C₁₀ alkane producthas an iso/normal weight ratio of at least about 45 (under theconditions defined in Example 13).

The hydrocarbonaceous feed can be contacted with the catalyst in a fixedbed system, a moving bed system, a fluidized system, a batch system, orcombinations thereof. Reactors similar to those employed inhydrotreating and hydrocracking are suitable. Either a fixed bed systemor a moving bed system is preferred. In a fixed bed system, thepreheated feed is passed into at least one reactor that contains a fixedbed of the catalyst prepared from the aluminosilicate ZSM-12 zeolite ofthe invention. The flow of the feed can be upward, downward or radial.Interstage cooling can be performed, for example, by injection of coolhydrogen between reactor beds. The reactors can be equipped withinstrumentation to monitor and control temperatures, pressures, and flowrates that are typically used in hydrocrackers. Multiple beds may alsobe used in conjunction with compositions and processes of the invention,wherein two or more beds may each contain a different catalyticcomposition, at least one of which may comprise aluminosilicate ZSM-12of the present invention.

EXAMPLES

The following examples demonstrate but do not limit the presentinvention.

Comparative Example 1 Synthesis of ZSM-12 Zeolite UsingMethyltriethylammonium Chloride

This is a comparative example showing the preparation of impure ZSM-12when using methyltriethylammonium cation as sole organic component inthe reaction mixture, i.e., in the absence of a diquaternary dicationstructure directing agent.

105.6 g of sodium silicate solution (Fisher brand, 28 wt % SiO₂, 8.9 wt% Na₂O) was mixed with 104.4 g of deionized water inside a 600-mL Teflonliner. Next 40 g of a 75% methyltriethylammonium chloride solution(Sachem) was dissolved in 120.5 g of deionized water and mixed with thesilicate solution. Then 4.02 g of aluminum nitrate nonahydrate wasdissolved in 227.1 g of deionized water. The aluminum nitrate solutionwas then added to the silicate solution with continuous stirring to forma uniform suspension. Next 6.4 g of sulfuric acid (98%) was added to thesuspension and mixed to form a uniform gel. The gel was mixed for anhour. The liner was then sealed within a Parr Steel autoclave reactor.The autoclave was heated under static conditions to 155° C. over a 4-hrperiod and then allowed to remain at 155° C. for 80 hours. The solidproducts were recovered from the cooled reactor by vacuum filtration andwashed with copious quantities of water. The solids were then allowed todry in an oven at 95° C. for over 12 hours. The powder XRD pattern(FIG. 1) indicated the product was ZSM-12 with minor amounts of ZSM-5 asan impurity.

Direct Synthesis of Small Crystal Al-ZSM-12 Examples 2-6 Example 2

105.6 g of sodium silicate solution (Fisher brand, 28 wt % SiO₂, 8.9 wt% Na₂O) was mixed with 104.4 g of deionized water inside a 600-mL Teflonliner. Next, in a second step, 32 g of a 75% methyltriethylammoniumchloride solution (Sachem) and 11.02 g of1,6-bis(2,3-dimethylimidazolium)hexane dibromide salt were dissolved in122.5 g of deionized water, and this solution was mixed with thesilicate solution. Then 4.02 g of aluminum nitrate nonahydrate wasdissolved in 227.1 g of deionized water. The aluminum nitrate solutionwas added to the silicate solution with continuous stirring to form auniform suspension. Next 6.4 g of sulfuric acid (98%) was added to thesuspension and mixed to form a uniform gel. The gel was mixed for anhour. The liner was then sealed within a Parr Steel autoclave. Theautoclave was heated under static conditions to 155° C. over a 4-hrperiod and then allowed to remain at 155° C. for 80 hours. The solidproducts were recovered from the cooled reactor by vacuum filtration andwashed with copious quantities of water. The solids were then allowed todry in an oven at 95° C. for over 12 hours. The powder X-ray diffractionpattern indicated the product was pure ZSM-12. Peak broadening in theXRD pattern is entirely consistent with the small crystallite size asnoted hereinabove.

Example 3

Example 2 was repeated except 36.29 g of 75% methyltriethylammoniumchloride solution, 5.51 g of 1,6-bis(2,3-dimethylimidazolium)hexanedibromide salt, and 121.52 g of deionized water were used in the secondstep. The powder XRD pattern indicated the product was pure ZSM-12.

Example 4

Example 2 was repeated using 38.04 g of 75% methyltriethylammoniumchloride solution, 2.75 g of 1,6-bis(2,3-dimethylimidazolium)hexanedibromide salt, and 121 g of deionized water in the second step. Thepowder XRD pattern indicated the product was pure ZSM-12.

Comparative Example 5

Example 2 was repeated except 7.02 g of aluminum nitrate nonahydrate wasused (instead of 4.02 g of aluminum nitrate nonahydrate). The autoclavewas heated under static conditions to 155° C. over a 4-hr period andthen allowed to remain at 155° C. for 5 days. The powder X-raydiffraction pattern indicated the product was ZSM-12 with a traceimpurity of mordenite.

Example 6

Comparative Example 5 was repeated except instead of heating understatic conditions, the gel was mixed with an overhead stirrer at 75 rpm.The powder XRD pattern indicated the product was pure ZSM-12. The Si/Alratio of this preparation of aluminosilicate ZSM-12 was determined to be22.

Synthesis of Small Crystal Borosilicate ZSM-12 Examples 7-10 Example 7

3.49 g of an aqueous solution of 1,4-bis(trimethylammonium)butanedihydroxide ([OH]=0.86 mmol/g), 0.37 g of potassium iodide, and 7.71 gof deionized water were mixed together. Then 0.035 g of potassiumtetraborate decahydrate (KTB) was dissolved in the solution, and 0.90 gof CAB-O-SIL M-5 (Cabot Corporation) was added and mixed to form auniform suspension. The mixture was placed in a Teflon cup, capped, andplaced within a sealed 23-ml stainless steel Parr autoclave. Theautoclave was placed in a spit within an oven at 160° C. and mixed at 43rpm for 7 days. The reactor was removed from the oven, allowed to cool,and the solids were collected by filtration and washing with deionizedwater. The solids were then allowed to dry within an oven at 95° C. TheSi/B ratio of the product, measured by Inductively CoupledPlasma—Optical Emission Spectroscopy (ICP-OES), was 31.8.

Examples 8 and 9

Two preparations of borosilicate ZSM-12 were performed as in Example 7,except 0.07 g of KTB was used in one (Example 8) and 0.10 g of KTB wasused in the other (Example 9). The Si/B ratios of the products fromExample 8 and 9 were 34.7 and 28.0, respectively.

FIG. 3 shows the powder XRD patterns of the products from Example 7,Example 8 and Example 9, compared with that of a standard (conventional)ZSM-12. The broader peaks of the patterns for the B-ZSM-12 products ofExamples 7-9 are consistent with the smaller crystal sizes of eachpreparation. Interestingly, for the three samples in this series, itappears that the gel with the highest boron concentration yields azeolite product with the broadest diffraction peaks. FIGS. 4 and 5 showscanning electron micrographs (SEM) of the product of Example 8. Thecrystalline aggregates were ellipsoids about 1 μm long and 0.3-0.5 μm inwidth. The individual crystallites within each aggregate were fineneedles with a width in the range from about 30 nm to about 40 nm.

Example 10

5.94 g of an aqueous solution of 1,4-bis(N-methylpiperidinium)butanedihydroxide ([OH]=0.51 mmol/g), 0.37 g of potassium iodide, and 4.86 gof deionized water were mixed together. Then 0.035 g of potassiumtetraborate decahydrate (KTB) was dissolved in the solution, and 0.90 gof CAB-O-SIL M-5 was added and mixed to form a uniform suspension. Thegel was then heated as described in Example 7. The product of thispreparation was identified by powder XRD analysis as B-ZSM-12.

Example 11 Indirect Synthesis of Small Crystal Al-ZSM-12 from SmallCrystal B-ZSM-12

The small crystal B-ZSM-12 product from Example 8 was calcined to atemperature of 595° C. to remove the organic from the zeolite. Thecalcination was performed in a muffle furnace by heating in 4%oxygen/nitrogen at 1° C./min to 595° C. and maintaining the temperatureat 595° C. for 6 hours. 0.71 g of calcined zeolite was then added to 15mL of a 1M solution of aluminum nitrate in a Teflon liner. The Teflonliner was capped and sealed within a stainless steel Parr autoclave. Theautoclave was heated at 160° C. overnight. After cooling, the solidswere removed by filtration and washed with ˜500 mL of deionized water toprovide small crystal aluminosilicate ZSM-12.

FIG. 6 compares the powder XRD pattern for the product of thispreparation (Example 11) with that of the original (precursor) materialof Example 8. The shifts in the diffraction peaks to lower angles areconsistent with expansion of the zeolite lattice when aluminum isinserted into the framework. The Al-ZSM-12 product was then exchanged tothe ammonium form using the following procedure. 0.59 g of zeolite wasadded to a solution of 0.59 g of ammonium nitrate in 5.8 g of deionizedwater. The exchange was allowed to proceed overnight at 95° C. Thezeolite was then recovered by filtration and a second ammonium exchangewas carried out.

Example 12 Palladium Exchange of Indirectly Synthesized AluminosilicateZSM-12

After the ammonium-exchange of small crystal Al-ZSM-12 (Example 11), thezeolite was palladium-exchanged as follows. 0.59 g of the Al-ZSM-12 wasadded to a solution prepared by mixing 2.56 g of 0.156 N ammoniumhydroxide, 4.41 g of deionized water, and 0.59 g of a solution ofPd(NH₃)₄(NO₃)₂. The palladium solution was formed by dissolving 0.72 gof Pd(NH₃)₄(NO₃)₂ in 42.01 g of deionized water and 6.00 g of 0.148 Mammonium hydroxide solution. The pH of the resultant slurry was adjustedto 10.0 with drops of ammonium hydroxide. The exchange was allowed toproceed for 2 days. The solids were then recovered by filtration andallowed to dry. The palladium exchanged zeolite was then calcined in amuffle furnace by heating at 1° C./min to 482° C. and maintaining thetemperature at 482° C. for 3 hours. The catalytic activity of thecalcined palladium exchanged zeolite was tested for n-hexadecaneconversion (see, e.g., Example 13).

Example 13 Conversion of n-hexadecane Over Pd-exchanged Al-ZSM-12

Palladium-exchanged aluminosilicate ZSM-12 (Pd/Al-ZSM-12) preparedaccording to Example 13 was used for the selective isomerization ofn-hexadecane under the conditions of temperature, pressure, weighthourly space velocity (WHSV), and hydrogen inlet (MSCFB) as given inTable 9, infra.

Products were analyzed by on-line capillary gas chromatography (GC). Rawdata from the GC was collected by an automated datacollection/processing system and hydrocarbon conversions were calculatedfrom the raw data. Yields were expressed as weight percent product. Forthe purpose of this example, isomerization selectivity is defined as thepercentage of n-C₁₆ in the feed that is isomerized to isoparaffins inthe product.

The data are summarized in Table 9. For this sample, a temperature ofabout 282° C. (540° F.) was necessary for 94% conversion. At thistemperature, isomerization selectivity was 82.6 (17.4% cracking). Thisselectivity was somewhat lower than that observed in Example 13, butagain there was a strong preference for the production of dimethyl-C₁₄(>64%), as compared with monomethyl C₁₅, in the isoparaffindistribution. These data demonstrate that borosilicate ZSM-12(precursor) of the present invention can be successfully transformed,e.g., according to the procedure of Example 12, into an aluminosilicateacid catalyst for use in isomerization selective hydroconversionprocesses.

TABLE 9 Summary of n-C₁₆ conversion and selectivity at differenttemperatures for small-crystal Al-ZSM-12 Measured Data Temperature (°C.) 288 285 282 283 284 WHSV 1.55 1.55 1.55 1.55 1.55 Pressure (psig)1200 1200 1200 1200 1200 H2 Inlet, MSCFB 53.9 53.9 53.9 53.9 53.9 nC₁₆Conv. 98.3 97.4 94.4 95.7 96.4 nC₁₆ Tot Rate 6.34 5.62 4.47 4.86 5.13nC₁₆ Crack Conv. 28.4 23.7 16.4 18.5 20.2 nC₁₆ Crack Rate 0.52 0.42 0.280.32 0.35 Selectivity % Isomerization 71.1 75.7 82.6 80.7 79 TotalCracking 28.9 24.4 17.4 19.3 21 C⁴⁻ Cracking 3.2 2.7 1.8 2 2.2 C₅₊Cracking 25.8 21.8 15.6 17.4 18.9 C₅₊/C⁴⁻ 8.1 8.3 8.6 8.7 8.7 C₅₊C6/C₅₊% 23.85 23.51 22.57 22.57 22.92 C6 DMB/MP 0.12 0.12 0.1 0.1 0.12 i/nRatios C₄ i/n 3.12 3.08 3.01 3.04 3.09 C₅ i/n 3.57 3.58 3.52 3.59 3.62C₆ i/n 2.73 2.76 2.7 2.73 2.81 C₇ i/n 3.01 3.07 3.02 3.06 3.1 C₈ i/n 44.01 3.93 4 4.05 C₉ i/n 5.35 5.27 5.06 5.28 5.32 C₁₀ i/n 6.19 5.88 17.3947.42 16.6 C₁₁ i/n 5.51 5.27 4.91 5.23 5.56 C₁₂ i/n 5.75 5.12 4.37 4.634.77 C₁₃ i/n 4.64 3.93 3.05 2.92 3.41 C₄-C₁₃ i/n 4.12 4.05 3.93 4.114.16 Wt % product C₁-C₃ <1 <1 <1 <1 <1 C₄-C₆ <10 <10 <10 <10 <10 C₇-C₁₃19.59 16.65 12.07 13.44 14.52 iC₁₆ 71.06 75.61 82.56 80.63 78.96Unidentified 0 0 0 0 0 Isoparaffin distribution Dimethyl C₁₄ 79.6 74.866.3 69.1 71.3 6-,7-,8-MethylC₁₅ 7.8 9.8 13.4 12.3 11.4 5-MethylC₁₅ 3.74.5 6 5.5 5.1 4-MethylC₁₅ 2.9 3.6 4.7 4.3 4.1 3-MethylC₁₅ 3.2 3.9 5.14.7 4.3 2-MethylC₁₅ 2.8 3.3 4.5 4.1 3.8

What is claimed is:
 1. An aluminosilicate ZSM-12 molecular sieve, characterized as polycrystalline aggregates of needle-like crystallites, and wherein each needle-like crystallite has a width in the range of about 15 nm to about 25 and a length in the range from about 60 nm to about 80 nm, with average dimensions of the crystallites of about 20 nm by about 60 nm, wherein the molecular sieve has a composition, as-synthesized and in the anhydrous state, in terms of mole ratios, as follows: SiO₂/Al₂O₃ 30-100 (Q + A)/SiO₂ 0.015-0.06  M/SiO₂  0-0.1

wherein: (1) M is at least one element selected from Groups 1 and 2 of the Periodic Table; (2) Q is cationic 1,6-bis(2,3-dimethylimidazolium)hexane, and Q>0; and (3) A is a second nitrogen-containing structure directing agent, and A is greater than 0; the aluminosilicate ZSM-12 molecular sieve having an X-ray diffraction pattern substantially as shown in the following Table: 2 Theta d-spacing (Angstroms) Relative Intensity  7.51 ± 0.25 11.76 M  8.86 ± 0.25 9.98 W 14.81 ± 0.25 5.98 W 15.28 ± 0.25 5.80 W 18.75 ± 0.25 4.73 W 19.11 ± 0.25 4.64 W 20.03 ± 0.25 4.43 W 20.91 ± 0.25 4.25 VS 21.98 ± 0.25 4.04 W 22.42 ± 0.25 3.96 W 22.98 ± 0.25 3.88 W 23.24 ± 0.25 3.82 M 25.21 ± 0.25 3.53 W 25.78 ± 0.25 3.45 W 26.33 ± 0.25 3.38 W 26.86 ± 0.25 3.32 W 27.99 ± 0.25 3.19 W 29.33 ± 0.25 3.04 W 30.88 ± 0.25 2.89 W 35.71 ± 0.25 2.51 W 36.97 ± 0.25 2.43 W 38.57 ± 0.25 2.33 W.


2. The aluminosilicate ZSM-12 molecular sieve according to claim 1, wherein the SiO₂/Al₂O₃ mole ratio of the aluminosilicate ZSM-12 is in the range from 30 to about
 80. 3. The aluminosilicate ZSM-12 molecular sieve according to claim 1, wherein the SiO₂/Al₂O₃ mole ratio of the aluminosilicate ZSM-12 is in the range from 30 to about
 60. 4. A method for preparing aluminosilicate ZSM-12, comprising contacting, under crystallization conditions: (1) at least one source of silicon oxide; (2) at least one source of aluminum oxide; (3) at least one source of an element selected from Groups 1 and 2 of the Periodic Table; (4) hydroxide ions; and (5) 1,6-bis(2,3-dimethylimidazolium)hexane cations.
 5. The method according to claim 4, wherein the aluminosilicate ZSM-12 molecular sieve is prepared from a reaction mixture comprising, in terms of mole ratios, the following: SiO₂/Al₂O₃   30-100 (Q + A)/SiO₂ 0.03-0.8 M/SiO₂ 0.05-1 OH⁻/SiO₂  0.1-1 H₂O/SiO₂   20-80

wherein: (1) M is at least one element selected from Groups 1 and 2 of the Periodic Table; (2) Q is cationic 1,6-bis(2,3-dimethylimidazolium)hexane, and Q>0; and (3) A is a second nitrogen-containing structure directing agent, and A is greater than
 0. 6. The method according to claim 4, wherein the molecular sieve has, after calcination, an X-ray diffraction pattern substantially as shown in the following Table: 2 Theta d-spacing (Angstroms) Relative Intensity  7.51 ± 0.25 11.76 M  8.86 ± 0.25 9.98 W 14.81 ± 0.25 5.98 W 15.28 ± 0.25 5.80 W 18.75 ± 0.25 4.73 W 19.11 ± 0.25 4.64 W 20.03 ± 0.25 4.43 W 20.91 ± 0.25 4.25 VS 21.98 ± 0.25 4.04 W 22.42 ± 0.25 3.96 W 22.98 ± 0.25 3.88 W 23.24 ± 0.25 3.82 M 25.21 ± 0.25 3.53 W 25.78 ± 0.25 3.45 W 26.33 ± 0.25 3.38 W 26.86 ± 0.25 3.32 W 27.99 ± 0.25 3.19 W 29.33 ± 0.25 3.04 W 30.88 ± 0.25 2.89 W 35.71 ± 0.25 2.51 W 36.97 ± 0.25 2.43 W 38.57 ± 0.25 2.33 W.


7. A method for preparing aluminosilicate ZSM-12, comprising: (a) preparing a reaction mixture containing (1) at least one source of silicon oxide; (2) at least one source of boron oxide; (3) at least one source of an element selected from Groups 1 and 2 of the Periodic Table; (4) hydroxide ions; (5) cationic 1,4-bis(trimethylammonium)butane or cationic 1,4-bis(N-methylpiperidinium)butane as the structure directing agent; and (6) water; (b) maintaining the reaction mixture under crystallization conditions sufficient to form crystals of borosilicate ZSM-12; and (c) replacing boron in the framework of the borosilicate ZSM-12 with aluminum to provide aluminosilicate ZSM-12.
 8. The method according to claim 7, wherein the borosilicate ZSM-12 molecular sieve is prepared from a reaction mixture comprising, in terms of mole ratios, the following: SiO₂/B₂O₃ 10-100 X/SiO₂ 0.05-1    M/SiO₂ 0.1-1   OH⁻/SiO₂ 0.1-0.6  H₂O/SiO₂ 20-100

wherein M is at least one element selected from Groups 1 and 2 of the Periodic Table, and X is cationic 1,4-bis(trimethylammonium)butane or cationic 1,4-bis(N-methylpiperidinium)butane.
 9. The aluminosilicate ZSM-12 molecular sieve according to claim 1, wherein A is selected from the group consisting of tetraalkylammonium cations, cationic dimethylpyrrolidinium, cationic dimethylpiperidinium, cationic dimethylpyridinium, and mixtures thereof
 10. The aluminosilicate ZSM-12 molecular sieve according to claim 9, wherein A is a tetraalkylammonium cation.
 11. The aluminosilicate ZSM-12 molecular sieve according to claim 10, wherein the tetraalkylammonium cation is a methyltriethylammonium cation.
 12. The aluminosilicate ZSM-12 molecular sieve according to claim 10, wherein the tetraalkylammonium cation is a tetraethylammonium cation. 